From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6E35878F2E for ; Thu, 23 Oct 2025 21:10:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761253850; cv=none; b=Ys69a3JjkqSAermXdVGk1FAwvIf4UESzgWLBpgo6Zjwo5m1Z0KfLE2L9MjATh8/BTU+3o9TEqJ2lHogGPJSn2JKyMjoLSLj5HP616YAs+1c87Phxin75EDGZiHciDrajvk7Lo4gK6Y1p3awgnKvXueXr2fsUPUSD0iwPz3aSNgY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761253850; c=relaxed/simple; bh=ZeXj6RHOgJiffLwS5fM8bhz4WNccfTBQc+5AvcbfMB8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ja8NYw9QCLupywOaUEiC0qaQ8tIxNwRrh+l1P5f13DpTnVVAw6mYUEOsctn+Xuhk/9uh4cgR6ptW+dgNUzNbbaDbuh1JQU43nJVAzReXIzZDniyAOL9eH5lHuWdPQ9pNUCvW8Li1MJqsxyTyCpur4ZCHHFhpq8SRy0+GgprhO40= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=OVxq+t+q; arc=none smtp.client-ip=192.198.163.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="OVxq+t+q" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1761253848; x=1792789848; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=ZeXj6RHOgJiffLwS5fM8bhz4WNccfTBQc+5AvcbfMB8=; b=OVxq+t+qsxHJoPdozGgGTFvOZ07tUFDyr5QIHp+hs1l5b4Ta+V/EsSdm KGxFrtsPALRuOdmETRTsr/VXXguiiP2/kEmvlHEAwW3A98BOhv8y599Th sYS4iOrhgNQiNKJW/3JTnOpa3jqOfWq5zhnJB+GmfSXWUA4KRU8yrHwpl Zar5vEWyFiF56MrgNBgsOGBpw6HPenN9uRgoh94durqXJNDmivomr7KUy Ut7YDlDPWhx+FTPml4/akrP8OjlbzZaEqpW1T7YkVqvPFVejkiaB1yvgN mQpYFL95ZA24zKFkgMwLczmjs/d7zq6RazGjOSkLpgPiMrAY45+g+7aXy g==; X-CSE-ConnectionGUID: E8I7frBASkKfpFyy6Di37A== X-CSE-MsgGUID: rkoba6oOR+aELzgZdLXejQ== X-IronPort-AV: E=McAfee;i="6800,10657,11586"; a="63342477" X-IronPort-AV: E=Sophos;i="6.19,250,1754982000"; d="scan'208";a="63342477" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2025 14:10:48 -0700 X-CSE-ConnectionGUID: zgERDZQJSl+348MR+kVQ2Q== X-CSE-MsgGUID: V5IyUYd4RpqXuYm43kUzSg== X-ExtLoop1: 1 Received: from tfalcon-desk.amr.corp.intel.com (HELO [10.125.108.251]) ([10.125.108.251]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2025 14:10:47 -0700 Message-ID: Date: Thu, 23 Oct 2025 14:10:46 -0700 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 00/21] Runtime TDX Module update support To: Vishal Annapurve , Chao Gao Cc: "Reshetova, Elena" , "linux-coco@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "Chatre, Reinette" , "Weiny, Ira" , "Huang, Kai" , "Williams, Dan J" , "yilun.xu@linux.intel.com" , "sagis@google.com" , "paulmck@kernel.org" , "nik.borisov@suse.com" , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Ingo Molnar , "Kirill A. Shutemov" , Paolo Bonzini , "Edgecombe, Rick P" , Thomas Gleixner References: <20251001025442.427697-1-chao.gao@intel.com> <5b4c2bb3-cfde-4559-a59d-0ff9f2a250b4@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/23/25 13:31, Vishal Annapurve wrote: ... >> Admin logic to update TDX modules can be designed to either retry >> failed TDX module updates or to be more robust, adds some >> synchronization with VM creation attempts on the host. i.e. I think >> it's fine to punt this problem of ensuring the forward progress to >> user-space admin logic on the host. > Discussed offline with Erdem Aktas on this. From Google's perspective > "Avoid updates during updatesensitive times" seems a better option as > I mentioned above. > > To avoid having to choose which policy to enforce in kernel, a better > way could be to: > * Allow user space opt-in for "Avoid updates during updatesensitive times" AND > * Allow user space opt-in for "Detect incompatibility after update" as well OR > * Keep "Detect incompatibility after update" enabled by default based > on the appetite for avoiding silent corruption scenarios. I'd really prefer to keep this simple. Adding new opt-in ABIs up the wazoo doesn't seem great. I think I've heard three requirements in the end: 1. Guarantee module update forward progress 2. Avoid "corrupt" TD build processes by letting the build/update race happen 3. Don't complicate the build process by forcing it to error out if a module update clobbers a build One thing I don't think I've heard anyone be worried about is how timely the update process is. So how about this: Updates wait for any existing builds to complete. But, new builds wait for updates. That can be done with a single rwsem: struct rw_semaphore update_rwsem; tdx_td_init() { ... + down_read_interruptible(&update_rwsem); kvm_tdx->state = TD_STATE_INITIALIZED; tdx_td_finalize() { ... + up_read(&update_rwsem); kvm_tdx->state = TD_STATE_RUNNABLE; A module update does: down_write_interruptible(&update_rwsem); do_actual_update(); up_write(&update_rwsem); There would be no corruption issues, no erroring out of the build process, and no punting to userspace to ensure forward progress. The big downside is that both the build process and update process can appear to hang for a long time. It'll also be a bit annoying to ensure that there are up_read(&update_rwsem)'s if the kvm_tdx object gets torn down during a build. But the massive upside is that there's no new ABI and all the consistency and forward progress guarantees are in the kernel. If we want new ABIs around it that give O_NONBLOCK semantics to build or update, that can be added on after the fact. Plus, if userspace *WANTS* to coordinate the whole shebang, they're free to. They'd never see long hangs because they would be coordinating. Thoughts?